The specific objective of the applicants is to develop a prototype HIV vaccine which targets in situ recruited or systemically expanded dendritic cells (DC) to act as antigen presenting cells (APC) for the activation of cytotoxic T cells. DC are a critical component of an effective vaccine as they are capable of sensitizing naive T cells, eliciting therapeutic immune responses, and overcoming tolerance. The hypothesis to be tested is that optimal CTL induction by an AIDS vaccine requires systemic DC expansion and the intravenous (i.v.) delivery of a particulate vaccine. The proposed studies will focus on the recruitment and expansion of DCs, and the development of a targeting strategy to improve delivery of the antigen to the DCs. The applicants plan to compare vaccine strategies using growth factors to recruit DC to the vaccine site (GM-CSF) or expand them systemically (flt3-L), in combination with antigen conjugates and formulations to enhance vaccine targeting to the DCs. HGP-30 (a relatively conserved region of HIV p-17) will be the antigen used in these studies as it has been shown that human volunteers vaccinated with HGP-30 develop peripheral blood mononuclear cells which can protect SCID mice against HIV challenge. Vaccine formulations (alum adsorbed or liposome encapsulated) with HGP-30 alone will be compared to HGP-30 conjugated to a peptide representing either the cell-binding peptide of beta-2-microglobulin of IL-1B to increase delivery to or activation of DCs. The Specific Aims of the proposal are to: (1) determine whether systemic expansion or local recruitment of DCs and vaccine delivery results in the systemic induction of cytotoxic T lymphocytes; (2) evaluate and compare the immunogenicity and DC targeting potential of HGP-30, HGP-30-B2m, and HGP-30-IL-1B heteroconjugate vaccines; and (3) evaluate the immunogenicity of heteroconjugate pulsed human DCs for the primary induction and expansion of human CTL and the protective activity of these CTL in SCID mice to HIV challenge.